(a) Field of the Invention
The present invention relates to an image display method and system for a plasma display panel. More particularly, the present invention relates to an image display method and system for a plasma display panel that reduces flicker and contour noise generated in a low gray region when an image is realized by the input of 50 Hz Phase Alternating by Line (PAL) image signals.
(b) Description of the Related Art
A plasma display panel is a display device in which a plurality of discharge cells are arranged in a matrix, and the discharge cells are selectively illuminated to restore image data, which are input as electrical signals.
In such a plasma display panel, the display of gray must be possible in order to exhibit the capabilities of a color display device. A gray realization method is used to achieve this, in which a single field is divided into a plurality of sub-fields and the sub-fields are controlled by a process of time sharing.
A major concern for the designer of display devices is that of flicker. Flicker is closely related to how the human eye perceives images. Generally, flicker becomes more perceptible as screen size is made larger and frequency is lowered. In the case where images are realized in a plasma display panel using PAL image signals, both these factors are present such that a significant amount of flicker is generated.
Accordingly, if the plasma display panel is driven at a vertical frequency of 50 Hz using a minimum increase arrangement or a minimum decrease arrangement, which are sub-field arrangements typically used in plasma display panels, a significant amount of flicker is generated.
Among the two factors that make flicker more problematic, since it is not possible to change the screen size, flicker must be reduced by varying frequency. Korean Laid-open Patent No. 2000-16955 discloses a method of reducing flicker by adjusting frequency. In this disclosure, to reduce flicker in a plasma display panel having a large screen and operated by the input of 50 Hz image signals, sub-fields within a single field are divided into two groups (G1 and G2), and a weight arrangement of the sub-fields in each group is identical or all sub-field arrangements except an Least Significant Bit (LSB) sub-field have the same structure. Further, a feature of this disclosure is that a brightness weighting value in the two sub-field groups are identically distributed. The reduction of flicker with the use of this method is greatly improved over the conventional sub-field arrangement of a minimum increase arrangement or a minimum decrease arrangement.
FIG. 1 is a schematic view of a conventional sub-field arrangement, and FIG. 2 is a schematic view showing an example of realizing specific low grays using the conventional sub-field arrangement. As shown in the drawings, in the case where low grays, for example, low grays 0 to 11, are displayed using the conventional sub-field arrangement, a time difference of a few milliseconds occurs between sub-fields corresponding to a LSB and a LSB+1.
For example, in the case of the low gray 3, lowermost sub-field SF1 of group G1 is On and lowermost sub-field SF1 of group G2 is also On. In this case, the sub-field of group G1 becomes a LSB sub-field and the sub-field of group G2 becomes a LSB+1 sub-field, with a time difference between the sub-fields being a substantial 10 ms.
Low brightness illumination characteristics for a plasma display panel are non-linear. To compensate for the non-linear gray characteristics, an error diffusion method is used to display low brightness grays. However, with use of the conventional sub-field arrangement and application of error diffusion to display low grays, a time difference between the sub-fields corresponding to an LSB and an LSB+1 is as much as a few milliseconds. Since an illumination acceleration time of illumination having this time difference is short, it becomes perceptible to the human eye such that if there is movement in the image, severe contour noise develops at boundaries between grays.